Electrodeless light source having improved arc shaping capability

Abstract

An electrodeless lamp is positioned at the end of an inner and outer conductor forming a termination fixture, the inner conductor being shaped such that the arc within the lamp during excitation is isolated from the wall of the lamp envelope. The inner conductor may be formed as a hollow helical element thereby providing both an axial and azimuthal electric field component. Alternatively, the inner conductor may be cup-shaped which has a shielding effect to control the electric field strength at the end of the conductor. The helical or cup element and other features of the inner conductor provide both arc shaping and impedance matching between the complex impedance of the lamp during operation and the output impedance of a high frequency power source which is coupled to the termination fixture.

We claim: 
     
       1. A light source including, a. a source of power at a high frequency,   b. an electrodeless lamp having an envelope made of a light transmitting substance and a volatile fill material enclosed within the envelope, the fill material emitting light upon breakdown and excitation;   c. a termination fixture having an inner conductor and an outer conductor disposed around the inner conductor, the conductors having a first end which couples power to the lamp and a second end which is coupled to the source; and   d. means operatively associated with the fixture for shaping the arc within the lamp during excitation so that the arc does not attach to the interior wall of the envelope thereby enhancing the life of the electrodeless lamp.   
     
     
       2. The light source according to claim 1, wherein the arc shaping means includes means in the region of the first end for controlling the magnitude of the power gained electrically in the region adjacent to the interior wall of the lamp envelope such that the power gained electrically in that region is not greater than the power in that region lost as heat. 
     
     
       3. The light source according to claim 2, wherein the power has a frequency ranging from 902 MHz to 928 MHz and wherein the conductors are circular in cross section and disposed concentrically with respect to each other. 
     
     
       4. A method of producing light including the steps of: a. placing an electrodeless lamp at the ends of a pair of conductors comprising an inner conductor and an outer conductor disposed around the inner conductor, the lamp having an envelope made of a light transmitting substance and a volatile fill material enclosed within the envelope, the fill material emitting light upon breakdown and excitation;   b. applying power at a high frequency to the other ends of the conductors to excite the fill material thereby producing an arc within the envelope and   c. shaping the arc within the envelope so that the arc does not attach to the envelope, thereby enhancing the life of the electrodeless lamp.   
     
     
       5. The method according to claim 4, wherein the step of shaping the arc includes controlling the magnitude of the difference between the power gained electrically P e  and the power lost as heat P h  in a region near the envelope such that P h  is equal to or greater than P e . 
     
     
       6. The method according to claim 5, wherein the step of controlling the power difference includes the step of limiting the magnitude of the electric field strength in said region thereby reducing the power gained electrically in the region. 
     
     
       7. The method according to claim 6, wherein the step of limiting the field strength includes the step of shaping the geometry of the end of the inner conductor which is in contact with the lamp.